Glycoprotein synthesis

Method for synthesis of a glycoprotein, the method comprising: a) incorporating into a protein an unnatural amino acid comprising a first reactive group; wherein the incorporation step comprises incorporating the unnatural amino acid into the protein with a tRNA pair orthogonal / aminoacyl orthogonal-tRNA synthetase (O-tRNA / O-RS), where the O-tRNA recognizes a selector codon and It incorporates the unnatural amino acid into the protein in response to the selector codon, and wherein the ORS O-tRNA aminoacilan with the natural amino acid; and, b) contacting the protein with a saccharide residue comprising a second reactive group, wherein the first reactive group reacts with the second reactive group to attach the saccharide residue to unnatural amino acid, thereby producing the glycoprotein.